Severe Thunderstorm Warning 9, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
225 PM CDT SUN APR 04 2010

.SYNOPSIS...
EASTERN IOWA...MO...IL..AND SOUTHERN WI REMAIN IN A MOIST WARM
ADVECTION PATTERN AHEAD OF A PROGRESSIVE TROF...CURRENTLY BISECTING
IOWA. ONE SHORT WAVE OVER THE UPPER GREAT LAKES HAS ALREADY HELPED
BRING ONE ROUND OF SHOWERS AND THUNDERSTORMS...WITH UP TO NICKEL
SIZE HAIL TO THE SOUTHEAST 1/2 TO 1/3 OF THE CWA LATE THIS MORNING
AND EARLY AFTERNOON. THE NEXT AND MORE IMPORTANT SHORT WAVE FOR THE
AREA IS LOCATED IN EASTERN NE AS OF 2 PM...AND IS SPREADING ANOTHER
PLUME OF SURFACE MOISTURE NORTHWARD INTO SOUTHEAST IOWA AT THIS TIME.
..ERVIN..
&&

.SHORT TERM...TONIGHT AND MONDAY...
A THUNDERSTORM EVENT...WITH SUPERCELL POTENTIAL FOR MAINLY LARGE
HAIL WILL EXIST LATE THIS AFTERNOON AND THIS EVENING AS THE NEBRASKA
SHORT WAVE MOVES EAST.  THIS EVENT SHOULD AFFECT ROUGHLY THE
SOUTHEAST 1/2 OF THE CWA...AND COULD PROVIDE SEVERAL HOURS OF ACTIVE
SEVERE WEATHER THROUGH 9 PM. THE STORMS SHOULD BE PROGRESSIVE AND BE
EAST OF THE AREA BY MID EVENING...REVEALING A QUITE REMAINDER OF THE
NIGHT. QPF VALUES WILL BE FORECAST FOR 0.25 OR LESS...BUT ANY
TRAINING STORMS THIS EVENING COULD PRODUCE MUCH HIGHER
AMOUNTS...WHICH IS MORE EXPLICITLY REPRESENTED IN THE GFS AND SPC
4KM WRF RUNS.  DAMAGING WINDS ARE ALSO POSSIBLE THIS EVENING...BUT
ARE EXPECTED TO BE QUITE ISOLATED DUE TO A SHALLOW STABLE BOUNDARY
LAYER.

AFTER A QUIET START TO MONDAY...THE TROF NOW TO THE SOUTH IS
EXPECTED TO LIFT NORTH OR REDEVELOP AS A WARM FRONT MONDAY
AFTERNOON. WITH A CAPPED WARM SECTOR AND THETA E ADVECTION OVER TOP
THE FRONT...ANOTHER ROUND OF POTENTIALLY STRONG STORMS IS POSSIBLE
MONDAY AFTERNOON. POPS WILL REMAIN IN CHANCE RANGES...AS THE TIMING
OF THE NEXT SHORT WAVE IS NOT WELL AGREE UPON. HOWEVER...ONCE THIS
EVENT BEGINS...IT WILL LIKELY CONTINUE RIGHT ON INTO MONDAY NIGHT.
SHEAR WILL BE SUFFICIENT FOR SUPERCELLS...AND IF THERE IS ANY
AVAILABLE SFC BASED CAPE WE MAY BE DEALING WITH A WIND AND TORNADO
THREAT FOR DISCRETE CELLS IN THE SOUTH MONDAY AFTERNOON. THIS WILL
BE MUCH MORE APPARENT AS GET CLOSER TO THE EVENT.

TEMPERATURES TONIGHT SHOULD COOL NICELY WITH CLEARING BEHIND THE
SHORT WAVE AND STORMS....INTO LOWER TO MID 40S.  MONDAY...WITH PCPN
HOLDING OFF TILL THE AFTERNOON...HIGHS SHOULD REACH THE MID TO UPPER
60S NORTH TO MID 70S SOUTH.
..ERVIN..

.LONG TERM...MONDAY NIGHT THROUGH NEXT SUNDAY...
FORECAST FOCUS ON SEVERE WEATHER AND HEAVY RAIN MONDAY NIGHT THROUGH
TUESDAY NIGHT. SIGNIFICANT SEVERE WEATHER OUTBREAK LOOMING.

VERY DYNAMIC SYSTEM WITH RICH GULF MOISTURE...FRONTAL BOUNDARIES
AROUND AND IMPRESSIVE DEEP LAYER SHEAR ALL COMING TOGETHER ACROSS
THE REGION MONDAY NIGHT THROUGH TUESDAY NIGHT. HAVE NOT MENTIONED
SEVERE OR HEAVY RAIN WORDING IN THE GRIDS/ZFP JUST YET BUT THIS WILL
NEED TO BE STRONGLY CONSIDERED FOR LATER SHIFTS.

MONDAY NIGHT...SUPERCELLS SHOULD BE ALREADY ONGOING FROM MONDAY
AFTERNOON CONTINUING INTO THE EVENING. LARGE TO VERY LARGE HAIL A
THREAT DUE TO ELEVATED STORMS NORTH OF THE WARM FRONT WHICH SHOULD
BE SITUATED ACROSS OUR NORTHERN CWA BY MONDAY NIGHT. HOWEVER ANY
STORM FORMING NEAR THE BOUNDARY THAT BECOMES SURFACE BASED WOULD
SUGGEST A TORNADO...POSSIBLY STRONG...AND WIND DAMAGE THREAT.
HELICITY VALUES MONDAY EVENING ARE ENORMOUS. THE BIGGEST QUESTION IS
WHERE THE WARM FRONT ENDS UP MONDAY NIGHT ESPECIALLY WITH ALL THE
CONVECTION EXPECTED. THE ECM KEEPS THE BOUNDARY STALLED ACROSS OUR
NORTHERN CWA WHILE THE GFS WANTS TO KEEP MOVING THE FRONT WELL TO
OUR NORTH. THIS HAS MAJOR IMPLICATIONS BECAUSE OF THE HEAVY RAIN
THREAT IF FRONT STALLS...AS 50-60 KNOT LOW LEVEL JET RAMS INTO THE
AREA ALL NIGHT LONG. SUPERCELLS IN THE EVENING SHOULD EVENTUALLY
EVOLVE INTO A RATHER LARGE MCS DURING THE NIGHT WITH CONTINUED LARGE
HAIL THREAT.

TUESDAY/TUESDAY NIGHT...DEEPENING TROUGH OUT WEST APPROACHES AND SO
DOES THE SURFACE LOW. WITH CONTINUED STRONG LOW LEVEL JET POINTED AT
OUR CWA THUNDERSTORMS SHOULD KEEP FIRING NORTH OF WHEREVER THE
FRONTAL BOUNDARY EXISTS...WHICH IS QUESTIONABLE AT THIS TIME. THE
ECM/GFS WANT TO KEEP THE BULK OF THE DVN CWA IN THE CAPPED WARM
SECTOR MOST OF TUESDAY...WITH MINIMAL CONVECTION. IF THERE IS ENOUGH
SUNSHINE TEMPS MAY JUMP INTO THE 80S BUT FOR NOW WILL KEEP MAX
READINGS WELL INTO THE 70S. AS LARGE SCALE ASCENT MOVES IN FROM THE
WEST AS DEEP TROUGH APPROACHES...ALONG WITH THE SURFACE LOW AND
STRENGTHENING COLD FRONT...INTENSE CONVECTION SHOULD DEVELOP BY
TUESDAY EVENING AS THE CAP WEAKENS CONSIDERABLY. FORECAST SOUNDINGS
INDICATE STRONG WIND FIELDS BUT UNIDIRECTIONAL. THIS SUGGESTS
DAMAGING WINDS AND LARGE HAIL THE MAIN THREAT. HOWEVER...TORNADO
THREAT WILL EXIST NEAR THE TRIPLE POINT AS THE SURFACE LOW TRACKS
FROM CENTRAL IOWA INTO NORTHERN ILLINOIS.

WEDNESDAY THROUGH SUNDAY...GFS DEVELOPS ANOTHER LOW PRESSURE WAVE
ALONG THE FRONT IN THE SOUTHERN PLAINS...WHICH MOVES INTO INDIANA ON
WEDNESDAY. THIS SPREADS MORE RAIN INTO THE DVN CWA POTENTIALLY
KEEPING US WET UNTIL THURSDAY MORNING. MAINLY DRY AND PLEASANT
THEREAFTER THROUGH SUNDAY.

..HAASE..

&&

.AVIATION...
A TROF OF LOW PRESSURE WILL MOVE EAST THROUGH THE TAF SITES TONIGHT.
THUNDERSTORMS ARE LIKELY TO AFFECT MLI AND BRL THROUGH 03Z...WITH
BRIEF IFR CONDITIONS. OTHERWISE...EXPECT VFR WEATHER AT CID AND
DBQ...AND FOLLOWING THE STORMS...MLI AND BRL SHOULD BE VFR THROUGH
MONDAY NOON. MONDAY AFTERNOON...A SCATTERED THUNDERSTORM THREAT IS
POSSIBLE AT ALL TAF SITES. ..ERVIN..

&&

.HYDROLOGY...
WITH PORTIONS OF THE MS RIVER SOUTH OF NEW BOSTON CURRENTLY IN MINOR
FLOOD AND OTHER TRIB RIVERS NEAR ACTION STAGE ANY HEAVY RAIN WOULD
AGGRAVATE OR RENEW THE RIVER FLOODING. A WIDESPREAD RAINFALL OF AT
LEAST 1 TO 3 INCHES MONDAY THROUGH TUESDAY NIGHT APPEAR REASONABLE
GIVEN THAT PRECIPITABLE WATERS ARE FORECAST BY THE NAM/GFS TO ABOUT
1.50 INCHES. IF THUNDERSTORMS TRAIN OVER THE SAME AREA FOR SEVERAL
HOURS THEN QPF AMOUNTS MAY BE EVEN HIGHER. FLASH FLOOD GUIDANCE FOR
1 AND 3 HOURS CURRENTLY IS ONLY 1 TO 2 INCHES SO THIS WILL NEED TO
BE MONITORED. A FLASH FLOOD WATCH MAY BE NEEDED AT SOME POINT FOR
EARLY THIS WEEK.
..HAASE..

&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.

&&

ERVIN/HAASE/ERVIN/HAASE

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
524 AM CDT SUN APR 4 2010

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-051030-
BUCHANAN-DELAWARE-DUBUQUE-BENTON-LINN-JONES-JACKSON-IOWA-JOHNSON-
CEDAR-CLINTON-MUSCATINE-SCOTT-KEOKUK-WASHINGTON-LOUISA-JEFFERSON-
HENRY IA-DES MOINES-VAN BUREN-LEE-JO DAVIESS-STEPHENSON-CARROLL-
WHITESIDE-ROCK ISLAND-HENRY IL-BUREAU-PUTNAM-MERCER-HENDERSON-
WARREN-HANCOCK-MCDONOUGH-SCOTLAND-CLARK-
524 AM CDT SUN APR 4 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL
ILLINOIS...NORTHWEST ILLINOIS...WEST CENTRAL ILLINOIS...EAST
CENTRAL IOWA...NORTHEAST IOWA...SOUTHEAST IOWA AND NORTHEAST
MISSOURI.

.DAY ONE...TODAY AND TONIGHT

THERE IS A CHANCE FOR SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO
EARLY EVENING. THE AREA OF GREATEST POTENTIAL IS ALONG AND SOUTH OF
A LINE FROM FAIRFIELD...THROUGH THE QUAD CITIES...TO PRINCETON
ILLINOIS WHERE THE STORM PREDICTION CENTER HAS PLACED A SLIGHT RISK.
THUNDERSTORMS ARE EXPECTED TO DEVELOP AFTER 3 PM ALONG A COLD FRONT
IN THIS AREA. THE GREATEST SEVERE WEATHER THREATS ARE DAMAGING WIND
GUSTS AND HAIL AROUND 1 INCH IN DIAMETER. STRONG WIND SHEAR MAY LEAD
TO A FEW SUPERCELL THUNDERSTORMS...AND AN ISOLATED TORNADO CANNOT BE
RULED OUT.

WARM TEMPERATURES...STRONG WINDS...LOW RELATIVE HUMIDITIES...AND
DRIED VEGETATION WILL COMBINE TO RESULT IN A VERY HIGH THREAT OF
GRASS FIRES THIS AFTERNOON.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

A SLOW MOVING UPPER LEVEL TROUGH AND DEVELOPING SURFACE LOW PRESSURE
SYSTEM WILL BE THE FOCUS FOR POTENTIAL SEVERE THUNDERSTORMS MONDAY
THROUGH TUESDAY.

A WARM FRONT WILL MOVE INTO THE AREA MONDAY AND PROVIDE A FOCUS
FOR POTENTIALLY SEVERE THUNDERSTORMS. IF SOLAR HEATING
SUFFICIENTLY DESTABILIZES THE ATMOSPHERE DURING THE AFTERNOON AND
EARLY EVENING...SHEAR WILL BE STRONG ENOUGH TO SUPPORT DEVELOPMENT
OF SUPERCELL THUNDERSTORMS. THE GREATEST SEVERE THREAT WOULD BE
IN CLOSE PROXIMITY TO THE WARM FRONT...AND STORMS COULD BE CAPABLE
OF PRODUCING LARGE HAIL AND TORNADOES.

STORMS WILL CONTINUE OVERNIGHT FUELED BY A STRONG LOW-LEVEL JET.
AS THE SURFACE LOW MOVES CLOSER TO THE AREA TUESDAY...THE SEVERE
WEATHER THREAT WILL RETURN WITH PASSAGE OF THE COLD FRONT. AT THIS
TIME...IT IS UNCLEAR WHETHER THE FRONT WILL MOVE THROUGH THE AREA
LATE TUESDAY AFTERNOON OR OVERNIGHT. IF IT MOVES THROUGH TUESDAY
AFTERNOON AND WE AGAIN GET SUFFICIENT SUNSHINE TO DESTABILIZE THE
ATMOSPHERE...SEVERE THUNDERSTORMS ARE POSSIBLE. IF THE FRONT MOVES
THROUGH OVERNIGHT WITHOUT BENEFIT OF DAYTIME HEATING...THE SEVERE
WEATHER THREAT WOULD BE LOWER.

.SPOTTER INFORMATION STATEMENT...SPOTTER ACTIVATION IS POSSIBLE
DURING THE NEXT THREE DAYS.

SHEETS/WOLF

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